The invention pertains to a method for controlling the process parameters of the working process of a glass forming machine, particularly an I.S. machine.
The production of hollow glass articles from molten glass in a glass forming machine by means of a shaping process, which is carried out on a prepared glass tear by means of a blank mold for producing a blank and a finish mold for producing a finished product and in which the finished product is transferred onto a conveyor belt leading into an annealing furnace via a dead plate, is characterized by several stations and transport processes, the respective operating parameters of which need to be adjustable and monitored with respect to a reproducible production result of constant quality. This applies to all parameters that influence the shaping process.
The quality of the hollow glass article produced in this way depends, in particular, on the stability of the entirety of all machine adjustments, the environmental conditions, the properties of the glass tear to be processed and of the article to be produced such as, among other things, its shape and the corresponding mass distribution of the glass. Other unavoidable interfering effects are caused by wear-related changes on machine elements, as well as environmental temperature fluctuations and frequently need to be counteracted with manual interventions in operating sequences. However, manual interventions are always dependent on the personal experience of the respective person carrying out the intervention, wherein machine adjustments are usually carried out such that a safety margin from critical adjustments is ensured. In many instances, this results in an incomplete utilization of the production capacity and therefore a reduction of the article throughput. The assurance of a constant product quality and the fullest possible utilization of the production capacity therefore are priority objectives for the operation of a glass forming machine.
According to DE 10 2006 003 330 A1, it is known to equip a glass forming machine with a thermal imaging camera that can be moved along the multiple stations in order to generate thermal images of the individual blank-molding tools and finish-molding tools that can be converted into control variables in a control device of a cooling apparatus such that individually adapted cooling air currents can be delivered to the individual molding tools, namely on the side of the blank molds, as well as on the side of the finish molds. In this way, the deformation conditions in the molding tools should be evened out, stabilized and optimized such that a uniform mass distribution of the glass in the produced glass article, a reduction of the required cooling air quantity and prolonged service lives of the molding tools can be achieved. The generation of the control variables is based on nominal values for the temperature of the molding tools stored in the control device such that the volume of the respective cooling air currents is adjusted in dependence on the deviation from these nominal values. This concerns a classic control circuit that, however, is only able to measure a partial aspect, namely the temperature ratios of the molding tools.
A similar method is known from EP 0 151 339 B1, wherein a thermal imaging camera can be pivoted about a vertical axis and respectively generate images of two stations of the glass forming machine in order to accelerate the imaging of the temperature ratios of the molding tools.
The method for controlling a glass forming machine known from DE 37 42 501 C2 is characterized in that the finished hollow glass product is inspected with respect to the presence of faults such as cracks or fissures after it has been cooled, wherein a fault signal that describes the detected fault is generated, the fault signals are analyzed in accordance with predefined and stored correction algorithms and the operating parameters of the glass forming machine are corrected in accordance with these algorithms. This correction is repeated with a time delay that is dependent on the manufacturing time and the cooling time. Corrective measures are taken with respect to the parameters of the blowing process in the respective mold and concern pressure changes, for example, of the blank blowing pressure or the final blowing pressure, changes of the blowing time, for example, of the blank blowing time, the final blowing time, etc., and temperatures such as, for example, a glass outflow temperature. This method is an iterative correction method that is executed automatically and intended to homogenize the quality of the produced hollow glass articles. However, this method does not function online such that the initiated corrective measures can only become effective with a certain time delay.
Due to an improved computer capacity, computer-assisted image analysis methods are becoming more and more popular as the basis for controlling the machine adjustments of glass forming machines because they make it possible to incorporate numerous influencing variables into the control algorithm.
For example, EP 1 418 158 A1 discloses a method and a device for controlling the quality of a glass tear in the shaping process of a glass forming machine, wherein a glass tear is in a free fall recorded by means of one or more cameras and a data set that describes a three-dimensional structure is generated, wherein this data set is compared with a corresponding stored standard data set with respect to the volume, surface shape, length, thickness, cut surface, etc. of the glass tear, and wherein machine adjustments are changed in dependence on this comparison, particularly on the type of deviation detected. In this quality control, a selection from several available machine parameters is therefore carried out in dependence on the type of deviation detected, namely the machine parameters that concern the glass tear formation, such that an intervention that is adapted to the type of the detected deviation from the standard data set can be realized.
EP 0 574 349 A1 discloses a method for monitoring the production sequence of a glass forming machine that is based on sensors in the form of IR cameras, CCD cameras, etc. and focuses, in particular, on fault sources in the cutting mechanism for a glass tear, the closure mechanism of the mold, the funnel mechanism for the supply of the molten glass, the level mechanism for the molten glass, as well as the dead plate. The image signals generated by means of the sensors upstream of a heater are analyzed in a computer-assisted fashion and this information is used for correcting possibly detected deficiencies. This control of machine adjustments is based on a nominal state of these adjustments.
U.S. Pat. No. 6,089,108 A discloses a device or an arrangement that is intended for use on the “hot end” of a glass forming machine and serves for optically measuring shaped-related parameters of hollow glass articles standing on a conveyor belt, namely by utilizing several cameras arranged in protective housings. These cameras are connected to a computer that is designed for additionally processing the image data generated by the cameras. This image data processing focuses on detecting misalignments of the individual hollow glass articles standing on the conveyor belt in the longitudinal and the lateral direction of the belt, as well as on carrying out a correction of the different size ratios of the cameras that record the hollow glass article from different viewing angles, such that an exact measurement of geometric parameters is realized despite these misalignments. This image data processing furthermore focuses on detecting an oblique axis of the hollow glass article relative to the horizontal support surface and on compensating potential motions of the hollow glass article relative to the support surface. However, this document merely aims to obtain information on the shape-related status of the hollow glass articles at an early stage on the hot end of the glass forming machine in order to discard articles with unacceptable shape-related parameters.
Document WO 2008/027569 A2 discloses a device that is intended for use in a system for molding plastic articles, in this case PET containers, in order to check the molded containers, namely by utilizing an arrangement of LED light sources, e.g. in the form of laser diodes, and photoreceivers in the form of sensors arranged opposite of the light sources. In this case, the transmission and the absorption behavior of the walls of the container is examined between the arrangements of light sources and sensors in two different wavelength ranges, wherein this examination focuses on the wall thickness of the containers, their mass, their volume and their material distribution. However, the signals received from the photoreceivers are primarily used for sorting out articles that do not meet defined standards based on the measuring results represented by these signals.
Another monitoring system for a glass forming machine that is based on a computer-assisted image analysis and intended for analyzing motion sequences is known from DE 10 2009 005 433 A1. In this case, one or more high-speed cameras are displaceably or pivotably arranged along the multiple I.S. stations and the image sequence of these cameras is used as the basis for detecting deviations from construction data, for preventive upkeep and maintenance work, for detecting a current state of wear, for reducing idle times and ultimately for control-technological interventions into the process sequence, among other things, in order to avoid time losses, to already detect damages at an early stage and to collectively achieve an increased throughput.
This prior art indicates that it was until now attempted to homogenize the product quality based on an analysis of the operating parameters of the glass forming machines such as, e.g., the molding tools, the glass tears to be formed or faults of the glass article in the form of cracks or fissures. However, intolerable aberrations detected in this way were always used exclusively for their correction insofar as a functional correlation exists between these aberrations and the operating parameters to be readjusted. This prior art is based on a measurement of temperatures in the region of the molding tools, of cooling air currents or of characteristic parameters that describe a glass tear, as well as on motion ratios.
In this context, however, properties of the produced hollow glass articles such as, e.g., deviations from a reference shape are not taken into account, wherein the mechanical stability of the hollow glass article that depends, among other things, on the mass distribution and is still low at the end of the shaping process due to comparatively high temperatures particularly needs to be taken into account. For example, each hollow glass article has its own temperature-dependent deformation behavior in dependence on the type of hollow glass article.
This prior art does not indicate that the thusly obtained information with respect to deviations between the shape of the hollow glass article and a reference shape was used in a control that focuses on eliminating the detected deviations.